<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
       
        
        .damao {
            width: 90px;
            height: 90px;
            background-color: red;
            float: left;
        }
        .ermao {
            width: 90px;
            height: 90px;
            background-color: gray;
            float: left;
        }
   
        .sanmao {
            width: 100px;
            height: 90px;
            background-color: greenyellow;
            float: left;
        }
        /* 清除浮动方法1--额外标签法，clear:both*/
        .clear {
            clear:both
        }
        .zhengchang {
            height: 150px;
            background-color: maroon;
        }
        
        
    </style>
</head>
<body>
    <div class="nav">
        <div class="damao">浮动1</div>
        <div class="ermao">浮动2</div>
        <div class="sanmao">浮动3</div>
        <!-- 新添加的标签必须是块级元素才可以，不能是行内元素 -->
        <div class="clear"></div>
        <div class="zhengchang"></div>
        
    </div>
</body>
</html>